After briefly outlining the work of William Withering (1741-1799) and Sir James Mackenzie (1853-1925) on the use of digitalis in the treatment of heart disease, the film describes the chemical composition and medicinal properties of the crystalline glycosides found in the leaves of the common foxglove (Digitalis purpurea), and shows how digoxin is extracted from the leaves of the white Danubian foxglove (Digitalis Lanata). The pharmacological action of digoxin is demonstrated on isolated rabbit and frog heart preparations and rabbit auricles, and clinical cases are used to show its therapeutic values in congestive heart failure. Animated diagrams are used to show the relation between cardiac action and electrocardiograms in the normal heart and in cases of auricular fibrillation, and to explain the therapeutic effects of digoxin. A patient with mild congestive heart failure is seen before and after treatment with digoxin. A severe case of congestive heart failure with auricular fibrillation receives digoxin intravenously and is also seen after treatment. 6 segments.